The present application claims priority under 35 USC 119 on Japanese patent applications No. 2000-017863, filed on Jan. 24, 2000, and No. 2000-081782, filed on Mar. 17, 2000, which are herein incorporated by reference.
1. Field of the Invention
The present invention relates to an image-recording material, more particularly to an image-recording material having high sensitivity and high storage stability and also to a method for recording an image by heat development using a heat-developable image-recording material.
The present technique can be applied to various industrial fields including films for printing plates, films for ordinary photographs, films for microphotographs, films for medical use, etc. and to materials for recording images by means of a camera or by exposure to a scanning laser beam.
2. Description of the Related Art
A method for forming an image using a heat-developable image-recording material with an organic acid silver salt is described in, for example, U.S. Pat. Nos. 3,152,904 and 3,457,075 and D. Klosterboer xe2x80x98Thermally Processed Silver Systems Axe2x80x99 (imaging Processes and Materials) Neblette, 8th edition, Ed. by J. Sturge, V. Walworth and A. Shepp, Chapter 9, p. 279 (1989). These photosensitive materials contain a reducible non-photosensitive silver source (e.g. an organic silver salt), a catalytic amount of a photocatalyst (e.g. a silver halide) and a reducing agent for silver which are usually dispersed in an organic binder matrix. While these photosensitive materials are stable at normal temperature, silver is produced through a redox reaction between the reducible silver source (functioning as an oxidizing agent) and the reducing agent when heated to a high temperature (e.g. 80xc2x0 C. or higher) after exposure. This redox reaction is promoted by the catalytic effect of the latent image formed by the exposure. The silver formed by the reaction of the reducible silver salt in the exposed area provides a black image, which contrasts with the non-exposed area, and an image is thus formed.
These photosensitive materials are generally formed by dispersing an organic silver salt and a silver halide, normally in a solution of an organic binder in an organic solvent, and adding a reducing agent dissolved in an organic solvent thereto. It is considered to be an essential requirement for the formation of an image that the silver halide is positioned so as to be in contact with the surface of the organic silver salt crystals. This is described in, for example, M. R. V. Sahyun, Thermally Developable Photographic Materials (TDPM): A Review of the State-of-the-Art in Mechanistic Understanding, J. Imaging Sci. Technology, 42, 23 (1998).
In recent years, heat-developable photosensitive materials containing an organic silver salt, a silver halide and a reducing agent using an aqueous dispersion of a thermoplastic polymer resin as a binder have been disclosed in JP-A-10-10669 and JP-A-10-10670. These image forming materials comprise a protective layer and a photosensitive layer in which an organic silver salt, a silver halide and a reducing agent are dispersed in a thermoplastic resin latex. In accordance with the above disclosure, a photosensitive silver halide is prepared beforehand, and the organic acid silver salt is crystallized in the presence of the silver halide grains. Although it is not specifically stated, it is surmised that the aim of the formation of the organic silver salt is to incorporate the silver halide crystals into the organic silver salt crystals so providing a state in which the organic silver salt and the silver halide are close to each other. This type of preparation method has been commonly employed among the above-mentioned systems using an organic solvent. Thus, the organic silver salt and the silver halide have been prepared so as to be close to each other, and they are inevitably coated in the same layer.
These heat-developable materials have an image formation layer of 10 xcexcm to 30 xcexcm, which is extremely thick in comparison with the ordinary wet process silver salt photographic materials, the photosensitive silver halide is thinly distributed among the organic acid silver salt grains, the exposure light path becomes long so increasing light scatter and absorption, and there is therefore the problem that the sensitivity and the resolution decrease. The photosensitive silver halide grains easily cause fogging in the presence of organic acid silver salt grains so resulting in the problem that the storage stability of the photosensitive material is degraded.
An objective of the present invention is thus to provide a heat-developable image-recording material having high sensitivity and excellent storage stability. It is also an objective of the present invention to provide a method for forming an image using the above-mentioned recording material.
In accordance with the above and other objectives, a first aspect of the present invention relates to a heat-developable image-recording material comprising, on a support, a silver-supplying layer containing an organic silver salt, a reducing agent, an organic binder and substantially no photosensitive silver halide, and a separate photosensitive layer containing a photosensitive silver halide, the heat-developable image-recording material further containing an electron-transfer agent.
In the present invention xe2x80x9csubstantially no photosensitive silver halidexe2x80x9d means such amount of photosensitive silver halide in the silver-supplying layer that has no influence to a formation of silver image in an interface between the silver-supplying layer and the photosensitive layer upon heat-developing after image-wise exposure. In the present invention the amount of photosensitive silver halide in a silver-supplying layer is, preferably 10 wt % or less, and more preferably 1 wt % or less, of a coated amount of photosensitive silver halide in a photosensitive layer of the heat-developable image-recording material. Most preferably, the silver-supplying layer of the present invention contain no photosensitive silver halide.
Although in the art the organic silver salt cannot be heat-developed unless the organic silver salt grains and silver halide grains are close to each other, the present inventor has found that, even when the two are present in separate layers, the use of the electron-transfer agent described in the present invention allows an image to be formed in the silver-supplying layer by exposure and development of the photosensitive layer.
A second aspect of the present invention relates to a method for forming an image by heat development comprising imagewise exposing a heat-developable image-recording material comprising, on a support, at least one silver-supplying layer containing an organic silver salt, a reducing agent, and an organic binder, and a separate photosensitive layer containing a photosensitive silver halide, the heat-developable image-recording material further containing an electron-transfer agent, and then heat-developing the heat-developable image-recording material, whereby development of the photosensitive layer forms a silver image in the silver-supplying layer.
The silver-supplying layer preferably contains no photosensitive silver halide. The silver-supplying layer preferably contains a halogen precursor. The photosensitive layer preferably contains a reducing agent. The organic binder is preferably formed from a polymer latex dispersed in an aqueous medium. The reducing agent is preferably used in the form of solid microparticles dispersed in an aqueous medium. The halogen precursor is preferably used in the form of solid microparticles dispersed in an aqueous medium. The electron transfer agent is selected from hydrazine derivatives, alkene derivatives, isoxazole derivatives and acetal compounds.
In accordance with the present invention, a heat-developable image-recording material having high sensitivity and excellent storage stability can be obtained.
FIG. 1 is a scanning electron micrograph of a cross section of a heat-developable image-recording material related to one embodiment of the present invention before heat development at a magnification of 3000 times.
FIG. 2 is a scanning electron micrograph of a cross section of a heat-developable image-recording material related to one embodiment of the present invention after heat development at a magnification of 3000 times.
FIG. 3 is a scanning electron micrograph of a cross section of a sample of a comparative heat-developable image-recording material before heat development at a magnification of 3000 times.
FIG. 4 is a scanning electron micrograph of a cross section of a sample of a comparative heat-developable image-recording material after heat development at a magnification of 3000 times.